The present invention relates to automobile antenna apparatus used on a vehicle body provided with a spoiler.
In recent years, from the point of view of design, a spoiler having a wing-shaped cross section is often placed on a vehicle body in order to increase the tire contact pressure during high speed running to thereby permit stable driving. FIG. 5 is a view showing the state where a spoiler 12 is placed at a roof end of a vehicle body 10 of a station wagon type. Likewise in a minivan type or a truck type, a spoiler 12 is often placed at a roof end. On the other hand, FIG. 6 is a view showing the state where a spoiler 12 is placed on a trunk of a vehicle body 10 of a sedan type. Likewise in a coupe type, a spoiler 12 is often placed on a trunk.
These spoilers 12 are mainly molded from insulating resin in order to save the weight or for any other purpose. Of them, there are some spoilers 12 having antenna apparatus disposed therein. FIG. 7 is a view showing an example of the structure of related-art antenna apparatus disposed in a spoiler 12. As shown in FIG. 7, the related-art antenna apparatus is constituted by a feeder element 14 formed into an L-shaped (L-type feeder element) in a spoiler 12, and a ground element 16 formed into an L-shaped likewise. The feeder element 14 and the ground element 16 are disposed substantially symmetrically. A signal line is electrically connected to the feeder element 14 through a coaxial cable or the like, while the ground element 16 is electrically connected to a vehicle body 10 serving as the ground. When the antenna apparatus is placed in the spoiler 12, the antenna apparatus does not project from the vehicle body 10 so as to be excellent in terms of design.
In the related-art antenna apparatus shown in FIG. 7, the pattern of the directivity in a horizontal plane with respect to vertically polarized signals is necked and nowhere close to a circle as shown in FIG. 8. The antenna apparatus can be hardly regarded as nondirectional. Thus, there is a problem that the sensitivity to AM broadcasting signals and FM broadcasting signals transmitted as vertically polarized signals varies widely in accordance with the direction of the antenna apparatus, that is, the direction of the vehicle body 10.
In the related-art antenna apparatus, both the feeder element 14 and the ground element 16 are long in horizontal size but short in vertical size inevitably because they are disposed in the spoiler 12. It can be therefore considered that a signal current flowing vertically through the feeder element 14 and the ground element 16 is limited so that nondirectivity cannot be obtained in a horizontal plane with respect to vertically polarized signals.